The invention relates to a device of the type described in the preamble of claim 1.
The bibliographic reference "DLG-Mitteilungen 7/1980, pages 393 to 398" describes technical methods for raising fish, according to which fish-raising facilities are divided into two groups, namely through facilities and recycled facilities. In contrast to through facilities, in which the water is used only once and is then drained out of the fish-raising facility, in recycled facilities the used water is recycled and then fed back into the fish pond.
Recycling of the water in recycled type facilities is performed in a bypass, either in an activated sludge pond with or without dip elements or in a drip element facility, like that known from biological wastewater purification. An important feature of this method of recycling the water is the removal of feces and sludge from the water, which is clarified before being returned to the fish pond. Settling tanks and/or screens are used for this purpose.
German OS 36 19 757 teaches a fish pond for intensive fish feeding and a method of operating a fish pond of this kind, whose essential feature consists in the simultaneous aeration and biological treatment of the water in a fish pond using the adhesive activated sludge method, whereby packing like that known from cooling tower technology is placed in a shaft located in the middle of the fish pond above aerating equipment, said packing serving as large-area inserts to absorb so-called biological turf, which is biologically processed according to the airlift pump principle by the water flowing through the shaft.
Without intermediate clarification, the water thus treated is returned through barrier screens to the fish part of the pond, while the feces and surplus sludge remain in the water and are kept suspended in the nonaerated fish part by the resultant flows and by the fish themselves. Enrichment of suspended matter in the fish pond is avoided by guiding water in a bypass through a settling pond where the materials that settle out are enriched and drawn off and the clarified water is returned to the fish pond.
The advantage of this known method over the method used in the through and recycled facilities lies in a much more frequent throughput of the fish pond water through the biological processing part and in a considerably reduced area requirement for the settling pond and/or a sludge filter.